Various grindstones have been proposed as a tool for grinding a workpiece. As one of these grindstones, a grindstone with abrasive grains arranged on one surface of a base is known (e.g., see Patent Document 1).
Patent Document 1 will be described on the basis of FIGS. 32(a) to 32(c).
As illustrated in FIG. 32(a), an upper surface 1102 of a base 1101 is covered by masks 1103 which are spaced apart from each other at a predetermined distance w. Then, as illustrated in FIG. 32(b), abrasive grains 1104 are disposed between the mask 1103 and the mask 1103, and are temporarily bonded to the base 1101 by a plating layer 1105. After temporary adhesion, the masks 1103 are removed, and then, as illustrated in FIG. 32(c), the base is again subjected to a plating process to mainly bond the abrasive grains 1104 to the base 1104, so that a grindstone 1110 is completed.
An outer diameter of the abrasive grain 1104 used for the grindstone 1110 is larger than the distance w of the masks 1103, as illustrated in FIG. 32(b). Since the outer diameter of the abrasive grains 1104 is larger than the predetermined distance w, the abrasive grains 1104 are temporarily bonded in a state in which vertexes 1111 protrude upward. The temporarily bonded abrasive grains 1104 are mainly bonded in the state in which the vertexes 1111 protrude upward, as illustrated in FIG. 32(c).
As the vertexes 1111 protrude upward, the workpiece to be ground by the grindstone 1110 comes in contact with the vertexes 1111. Two faces, between which the vertex 1111 is interposed, serve as a rake surface 1112 and a relief surface 1113 in an edged tool. As the two faces, between which the vertex 1111 is interposed, serve as the rake surface 1112 and the relief surface 1113, the workpiece can be effectively ground.
In order to manufacture the grindstone 1110, it is necessary to temporarily bond the abrasive grains in the state in which the masks 1103 are provided, and then, after the masks 1103 are removed, again mainly bond the abrasive grains. That is, since it is necessary to divide and provide the plating layers 1105 in two steps, the number of steps is increased.
In addition, Patent Document 2 discloses a grindstone in which a plurality of abrasive grains are bonded to a surface of a base in a state of the grains are arranged in pieces. In order to set a height from the surface of the base to a vertex of the abrasive grain, a top of the abrasive grains is removed through truing.
FIG. 33(a) is a view illustrating one example of the abrasive grains. An abrasive grain 2101 is formed in a polygonal shape. The abrasive grain 2101 is displaced on a surface of a base 2102, and then is bonded thereto by a plating 2103, as illustrated in FIG. 33(b), thereby manufacturing a grindstone 2103.
As illustrated in FIG. 33(c), as the grindstone 2104 is moved in a direction indicated by an arrow (1), a surface of a workpiece 2015 can be ground.
In FIG. 33(b), a direction of the abrasive grain 2101 is not controlled. That is, an upper surface 2106 may be parallel with the surface of the base 2102, or may be inclined to the surface.
If the upper surface 2106 is parallel with the surface of the base 2102, the upper surface 2106 comes in contact with the surface 2107 of the workpiece 2105, and thus grinding resistance is increased.
As a result, machining precision or a lifetime of the grindstone is deteriorated.
Meanwhile, in a grindstone 3100 includes a base 3101 and abrasive grains 3103 and 3104 which are bonded to an upper surface of the base 3101 by a plating layer 3102, as illustrated in FIG. 34, as vertex portions 3105 and 3106 of the abrasive grains of the grindstone 3100 are ground at a predetermined angle, relief surfaces 3108 and 3109 can be formed. Since the abrasive grains have the relief surfaces 3108 and 3109, the grindstone 3100 can effectively grind the workpiece.
It is believed that the abrasive grains 3103 and 3104 bonded to the upper surface of the grindstone 3100 are dispersed in a longitudinal direction (front and rear direction of the drawing) of the grindstone 3100, in addition to a width direction (left and right direction of the drawing).
If the abrasive grains are dispersed in the longitudinal direction (front and rear direction of the drawing), as illustrated in FIG. 35, an abrasive grain 3111 indicated by an imaginary line exists in front of the abrasive grain 3104. As described above, the abrasive grains 3104 and 3111 are formed with relief surfaces 3109 and 3112 on the same surface by the grinding.
Focusing on rake surfaces, a rake surface 3114 of the abrasive grain 3104 and a rake surface 3115 of the abrasive grain 3111 are not aligned with each other. That is, since the size, shape or position of the abrasive grains 3104 and 3111 is different from each other, the rake surfaces 3114 and 3115 are not aligned with each other.
A position of an edge portion positioned between the rake surface and the relief surface is not aligned.
It is also considered a method of machining the relief surface, as illustrated in FIG. 36. The grindstone 4110 is secured to a cylindrical rotating tool 4112, with grindstone pockets 4111 for receiving the grindstone 4110 being provided on its circumference. The grindstone 4110 includes a base 4113 and an abrasive grain 4114 bonded to the base 4113, and the abrasive grain is placed on a center line 4115 of the rotating tool 4112. The plurality of abrasive grains 4114 are aligned and disposed on the plurality of bases 4113 provided on the circumference of the rotating tool 4112.
A truing grindstone 4116 is displaced at a position in which the truing grindstone 4116 comes in contact with the abrasive grain 4114.
The relief surface is formed on the abrasive grain 4114 by approaching and bringing the truing grindstone 4116 into contact with the rotating tool 4112, which is positioned and fixed, at a slope of a predetermined angle θ of a radial line 4118 of the truing grindstone 4116 to the center line 4115 of the rotating tool 4112, while the truing grindstone 4116 is rotated as indicated by an arrow (3). After that, the rotating tool 4112 is rotated at a predetermined angle (90° in FIG. 37) and then is again positioned and fixed, and the relief surface is sequentially formed on the abrasive grains 4114 arranged and displaced on all bases 4113 on the circumference of the rotating tool 4112.
According to the method, however, in order to uniformly form the relief surface on the abrasive grains 4114 arranged and displaced on all bases 4113 on the circumference of the rotating tool 4112 at high precision, it is necessary to constantly maintain a center distance between the truing grindstone 4116 and the rotating tool 4112 when the truing grindstone 4116 comes in contact with the abrasive grains at the predetermined angle θ. Since the truing stone 4116 or the rotating tool 4112 is significantly large relative to the abrasive grain 4114, even a slight slippage in the predetermined angle θ or the center distance is not allowed. As a result, it is not possible to actually form the uniform relief surface of the high precision.